Diet therapy and exercise therapy are essential in the treatment of diabetes mellitus. When these therapies do not sufficiently control conditions of patients, insulin or anti-diabetic agents are used. Examples of the anti-diabetic agents include, at the present, biguanides, sulfonylureas, insulin-sensitizing agents and α-glucosidase inhibitors. However, these anti-diabetic agents have various side effects. For example, biguanides cause lactic acidosis, sulfonylureas cause significant hypoglycemia, insulin-sensitizing agents cause edema and heart failure, and α-glucosidase inhibitors cause abdominal bloating and diarrhea. Under these circumstances, new anti-diabetic drugs that eliminate these side effects are desired.
Recently, it has been reported that hyperglycemia participates in the onset and progression of diabetes mellitus. This theory is called glucose toxicity theory. Namely, chronic hyperglycemia leads to decrease of insulin secretion and insulin sensitivity, the plasma glucose level is elevated, and as a result, diabetes mellitus is self-exacerbated [cf., Diabetologia, vol. 28, p. 119 (1985); Diabetes Care, vol. 13, p. 610 (1990), etc.]. Based on this theory, it is expected that normalization of plasma glucose level interrupts the aforementioned self-exacerbating cycle and the prevention or treatment of diabetes mellitus can be achieved.
It is considered that one method for the treatment of hyperglycemia is to excrete an excess amount of glucose directly into urine so that the blood glucose concentration can be normalized. For example, by inhibiting sodium-dependent glucose transporters being present at the proximal convoluted tubule of kidney, the re-absorption of glucose at the kidney is inhibited whereby the excretion of glucose into urine can be promoted and the blood glucose level can be decreased. In fact, it is confirmed that by continuous subcutaneous administration of an SGLT inhibitor, phlorizin, to diabetic animal models, the blood glucose level thereof can be normalized, and that by keeping the blood glucose level normal for a long time, the insulin secretion and insulin resistance can be improved [cf., Journal of Clinical Investigation, vol. 79, p. 1510 (1987); ibid., vol. 80, p. 1037 (1987); ibid., vol. 87, p. 561 (1991), etc.].
In addition, by treating diabetic animal models with an SGLT inhibitor for a long time, insulin secretion response and insulin sensitivity of the animal models are improved without incurring any adverse affects on the kidney or imbalance in blood levels of electrolytes, and as a result, the onset and progress of diabetic nephropathy and diabetic neuropathy are prevented [cf., Journal of Medicinal Chemistry, vol. 42, p. 5311 (1999); British Journal of Pharmacology, vol. 132, p. 578 (2001), etc.].
In view of the above, SGLT inhibitors are expected to improve insulin secretion and insulin resistance by decreasing the blood glucose level in diabetic patients and to prevent the onset and progress of diabetes mellitus and diabetic complications.
WO 2006/035796 discloses N-β-D-glycopyranosyl nitrogen-containing heterobicyclic compounds of the following formula:

The above compounds are described as SGLT1 and/or SGLT2 inhibitors and are useful for the prevention or treatment of diabetes and related diseases.